Method of agglomerating particulate material

ABSTRACT

A method of compacting particulate material into agglomerates, in which at least a portion of the cylindrical surface of at least one roll in a pair of compacting rolls is coated with a layer of particulate magnetic material which is retained on the roll surface by means of magnetic forces.

United States Patent 1 Gorling 1451 Feb. 18,1975

[54] METHOD OF AGGLOMERATING PARTICULATE MATERIAL [75] Inventor: Karl Giiran Giirling, Lidingo,

Sweden [73] Assignee: Boliden Aktiebolag, Stockholm, 7 Sweden [22] Filed: Apr. 18, 1972 21 Appl. No.: 245,173

52 US. Cl 264/24, 264/lll,264/l40 51 1111.01. ..H05b 1/00 58 Field of Search ..254/111,24, 140,22

[56] 1 References Cited UNITED STATES PATENTS 3,095,262 6/1963 Maish et al. 26 4/l1l 3,663,131 5/1972 Hegewaldt .Q 264/111 Primary Examiner-Robert F. White Assistant Examiner.l. R. Hall Attorney, Agent, or Firm-Stevens, Davis, Miller & Mosher 57 ABSTRACT 4 Claims, 11 Drawing Figures PATENTEB FEB 1 8 I975 snmag PAIEN FEB! 8 m SHEET 3 or 3 METHOD OF AGGLOMERATING PARTICULATE MATERIAL The present invention relates to a method of agglomerating particulate material by compacting the same between co-acting rolls.

It is previously known to agglomerate particulate material, e.g. in order to facilitate handling of the material and to convert it to a form which renders it convenient for use in subsequent processes. Such agglomerates can be produced in many different ways, of which one of the most economical isone in which the material is passed between two or more co-acting pressure rolls whose cylindrical surfaces may be either smooth or provided with a shallow pattern, such as an arrangement of shallow grooves for example, so that a continuous, substantially coherent cake of compacted material is obtained, which may be subsequently broken up into agglomerates of a desired size, or may be allowed to disintegrate into separate agglomerates independently. The cylindrical surface of such compacting rolls may also be provided with relatively deep grooves or patterns, in the form of cup-shaped recesses, for example, to enable separate agglomerates such as briquettes or the like to be formed directly. Agglomerating methods of the above type are described, for example, in Swedish Pat. Ser. Nos. 304,767,.319,500 and 332,645.

When applying the above mentioned methods of compacting granulate material, difficulties are sometimes experienced in maintaining a uniform and trouble-free flow of material to and between the rolls, owing to relative movement between the material to be agglomerated and the rolls or sliding of the material therebetween, or as a result of arching of the material above the rolls, whereby the material is prevented from flowing down into the roll nip. To overcome such diff culties, feeding devices are often used, usually in the form of one or more screw feeders which advance the material positively and force it towards the rolls and the nip therebetween. Although such feed devices reduce to some extent the problem of obtaining a uniform material flow, they are difficult to regulate and adjust in dependence of the roll pressure and the peripheral speed of the rolls, and hence the use of such feeding devices does not fully eliminate the problem of obtaining a uniform flow of material to and between the rolls, or fully prevent sliding of the material therebetween. In addition, sliding between the rolls of material which has been positively fed thereto by feeding devices is liable to cause considerable wear on the peripheral surface of the rolls.

When using smooth agglomerating rolls, irregularities formed in the surface of the rolls as a result of wear can be removed, while the rolls areworking, e.g. by planing or grinding downthe roll surface. If the rolls are homogeneous or, when hollow, have sufficient shell thickness, it is possible to perform a large number of such smoothing operations. Grinding and planing of the roll surfaces, however, incurs an additional expense and complicates the agglomerating method. Moreover, it does not contribute towards solving the problem of relative movement of sliding of the material between the roll surfaces. In, for example, Swedish Pat. Ser. No. 304,767 it has been proposed to protect smooth rolls by continuously coating the same with, for example, graphite or CaO, by applying to the rolls a layer of wearproof ceramic material, e.g; such materials based on aluminum oxide or carborundum, and by coating the rolls with the material to be agglomerated, i.e., autogeneous coating. According to the patent, the coating material can be continuously applied to the roll surfaces during an agglomerating operation, and the thickness of the formed coating can be adjusted by continuously or intermittently planing the roll surfaces or by any other appropriate machining operation. The use of a preformed protective coating does not solve the problem of sliding between the roll surfaces and the material being agglomerated. With regard to the proposed method of continuously coating the rolls as described in the above patent, this has proven difficult to effect in practice and cannot be relied upon to prevent sliding of the material between the rolls. When applying this latter method, it is often difficult in practice to avoid sliding between the continuously applied coating material and the roll surfaces, and in those instances when the coating material adheres to the roll surfaces it produces generally an uneven surface, which must be continuously smoothed off by turning, planing or by some other appropriate machining operation, thereby requiring the use of relatively complicated auxiliary apparatus, which are difficult to regulate and adjust in response to the rolling parameters.

The object of the present invention is to eliminate the aforementioned disadvantages associated with known roll agglomerating methods either completely or at least to a substantial extent, irrespective of whether smooth rolls are used or rolls having a shallow or deep pattern arranged on the cylindrical surfaces thereof. This object is achieved in accordance with the invention by the fact that at least one of the rolls is coated over at least a portion of its surface contacting the ma terial being compacted with a layer of particulate magnetic material which is retained on said portion of the 7 roll surface, by magnetic forces. ln this way, the magnetic material located nearest the roll surface will be attracted thereto, thereby increasing the frictional force between the surface and the material and eliminating or greatly reducing non-uniform flow of the material to and between the rolls and wear producing relative movement between the material and the roll surfaces. Further, the increased frictional 'force enables rolls of smaller diameter to be used than hitherto usual, whereby agglomeration of the particles can be effected with a lower pressure between the rolls and thus with the use of less robust and cheaper apparatus and, moreover, obviates the use of devices for positively feeding the material on the input side of the rolls, at least in some of those cases where such devices have been found necessary hitherto.

When agglomerating particulate magnetic material, such as sponge iron and certain products obtained from dust separating processes in metallurgical techniques, for example dust obtained from Kaldo and LD processes, magnetite, pyrrhotite and other fine grain ferromagnetic metal materials and minerals, at least a portion of the material to be agglomerated can be used in accordance with one aspect of the invention to form the aforementioned coating, while when agglomerating at least substantially non-magnetic particulate material,

such as hematite, hydrous iron ores and ores containing iron carbonates certain products from dust separating processes in metallurgical techniques and other fine, substantially non-magnetic metal minerals and materials, the cylindrical surface of the roll or rolls is prevented from coming into contact with the at least substantially non-magnetic material by successively applying the magnetic materialforming said coating to the roll surface. .In accordance with another aspect of the invention, when agglomerating substantially nonmagnetic material, the magnetic material forming the coating on the roll surface may be mixed directly with the substantially non-magnetic material. The method according to the invention has been found particularly suitable in connection with the agglomeration of roasted products obtained from the roasting of fine metal sulphides recovered, for example, by flotation techniques, particularly roasted products obtained by the methods described in Swedish Pat. Ser. Nos. 204,002 and 227,187, where a magnetic, fine product, comprising substantially magnetite, is obtained. A particularly suitablemethod of refining fine-grain iron sulphide is thus to roast the iron sulphide material in accordance with the methods described in the above patents, optionally together with hematitic material, to substantially magnetite, and then agglomerate the material in accordance with the method described in the accompanying claims.

The agglomerating apparatus used for carrying out the method of thepresen't invention includes at least two co-acting, contra-rotating pressure rolls and at least one means for guiding particulate magnetic material to the input side of the rolls, and is mainly characterized by means for maintaining a magnetic field in the materialand in at least one of the rolls over at least a portion of the region thereof within .which the material and the roll are incontact with each other.

The invention will now be described in more detail with reference to the accompanying drawings, further features of the'invention being disclosed in connection therewith. In the drawing, I

FIG. I illustratesdiagrammatically a cross sectional view of a first embodiment of an agglomerating rolling mill according to the invention, taken at right angles to the roll axes.

FIG. 2 is an axial sectional view of a portion of the roll in the agglomerating rolling mill of FIG. 1 provided with magnets.

FIG. 3 is a sectional view, similar to FIG. 1, of a second embodiment of the agglomerating rolling mill according to the invention.

FIG. 4 is a partial axial sectional view of one of the rolls-in the agglomerating rolling mill of FIG. 3.

FIG. 5 is a sectional view, similar to that of FIG. 1, of a third embodiment of the agglomerating rolling mill according to the invention, and

FIG. 6 is a partial axial sectional view of one of the rolls in the agglomerating rolling mill of FIG. 5.

FIGS. 7 and 8 are sectional views, similar to FIG. 1, of a fourth and a fifth embodiment respectively of the agglomerating rolling mill according to the invention.

FIG. 9 illustrates diagrammatically and in plan view a sixth embodiment of the agglomerating rolling mill according to the'invention.

FIG. 10 is av sectional view, similar to FIG. 1, taken through the line X X in FIG. 11 of a seventh embodiment of the agglomeratingrolling mill according to the invention, and

FIG. 11 is a diagrammatically horizontal sectional view of the agglomerating rolling mill according to FIG. 10 taken on the level of the roll axes.

In FIGS. 1, 3 and 5 and 7 11 the reference numeral 10 indicates two co-acting compacting rolls, which rotate in the direction shown by the arrows. The known devices for journalling and operating the rolls and the means for setting the desired roll pressure have been omitted from the drawing, since such means and de-' vices are well known to all skilled in the art and doriot form part of the present invention. As illustrated in FIGS. 1, 3, 5, 7, 8 and 10, means for guiding particulate material to the input side of the rolls are arranged immediately above the rolls 10, these means being identified with reference numeral 11 in FIGS. 1, 5, 7, 8 and 10 and with reference numerals l2 and 13 in FIG. 3. The guide means 11, 12, 13, which have the form of open end hoppers extending at least substantially along the whole length of the rolls 10, can be complemented in a known mannerwith feeding devices, such as feeding screws, which force the material towards the rolls 10. The material to be compacted or agglomerated is fed, preferably continuously, to the hoppers l 1, l2, 13 by means of suitable apparatus, for example an endless conveyor belt -14, as indicated in FIG. 1.

The material, shown at 15, processed in the agglomerating rolling mill of FIGS. 1 and 2 and advanced to the input side of the rolls by the conveyor belt 14 and the hopper 11 is ferromagnetic. The roll 10, illustrated to the right of FIG. 1 and shown in partial axial sectional view in FIG. 2, is provided with a number of axially arranged rod shaped permanent magnets 16 disposed peripherally of the roll. The magnets 16, which may extend in one piece along the totallength of the roll 10 or be-constructed of a number of individual parts, as shown with dash lines 17 in FIG. 2, are arranged between an outer, roll shell 18 comprising a material having low magnetic permeability, for example a nickel or manganese alloyed. austenitic steel, and an inner roll portion or core 19 comprising a material having high magnetic permeability, e.g. a ferritic steel. The magnets 16 are spaced apart in the peripheral extension of the roll and although the spaces between the magnets 16 may be left empty, it is preferred, as illustrated in FIG. 1, to fill the spaces with inserts 20 comprising a material of low magnetic permeability and arranged to support the roll shell 18. The direction of magnetization of the magnets 16 is suitably radial as seen in FIG. 1, the magnets 16 being arranged so that the north and south poles of consecutive magnets lie alternately adjacent the roll jacket 18. By this arrangement, thereis created a magnetic field in the roll 10 and in the magnetic material 15 located nearest the roll shell 18, whereby the magnetic material 15 located nearest the shell 18 isattracted to the roll'surface and the tendency of the material 15 to slide relative the lat-' ter roll 10 is either eliminated or at least greatly reduced. With the embodiment illustrated in FIG. 1, the roll 10 shown to the left of the Figure is not provided with magnets. This roll comprises a roll core 21 encircled by a shell 22, which may comprise a material having high magnetic permeability, whereby the magnetic field produced by the roll 10 provided with magnets is able to cause attraction of the material 15 to the roll 10 without magnets. For the purpose of controlling the supply of material 15 to the roll 10 provided with magnets, and thus also the thickness of the cake of compacted material, the hopper I1 is provided with a vertically sliding door 23. I

If, after being compacted, the material shows a tendency to stick to one or both rolls 10, eg when the material being agglomerated is such that the generally coherent cake disintegrates independently into small agglomerates upon leaving the roll nip, it is convenient to provide the embodiment illustrated in FIGS. 1 and 2, and also the embodiments illustrated in the remaining FIGURES, with means for removing at least the major portion of the material from the surface of the roll or rolls, e.g. as by scraping. Suitable means for this purpose are shown in FIG. '1 at 24. v

The agglomerating rolling mill according to FIGS. 1 and 2 has been described with reference to the agglomeration of magnetic material. It will be readily perce ived, however, that the agglomerating rolling mill of the present invention can also be used for agglomerating particulate material comprising a mixture of magnetic particles and particles which are at least substantially non-magnetic. When agglomerating particulate material of which the particles are predominantly nonmagnetic, it is preferred, however, to form on the rolls a'layer of magnetic material by means of magnetic forces, and tocompact-the nonmagnetic or substantially non-magnetic material between the rolls thus coated with magnetic material.

FIGS. 3 and 4 illustrate an agglomerating rolling mill whichoperates in accordance with this latter method. The rolls 10 are constructed in substantially the same manner as the roll 10 illustrated in FIGS! 1 and 2 having the magnets 16. Thus, the rolls of the embodiment illustrated in FIGS. 3 and 4 have a shell 18 comprising a material of low magnetic permeability and a core 19 of high magnetic permeability-Arranged radially and in spaced apart relationship between the shell 18 and the core 19 are ring shaped permanent magnets having a radial direction of magnetization and comprising separate ring segments 25, the magnets encircling the core 19 and being distributed along the whole length of the roll 10. The magnetic segments are arranged so that each alternate magnet has its north pole located adjacent the shell 18, while the remaining magnets have their south pole locatedadjacent said shell. As illustrated in FIG. 4, inserts 26 comprising a material of low magnetic permeability are arranged in the spaces between the segments 25, to support the roll shell 18. The magnetic material 15, which may comprise finegrained magnetite, for example, is passed to the rolls 10 from the hoppers 13 located on either side of a central hopper 12, from which substantially non-magnetic material 27 such as fine-grained hematite is supplied to the rolls 10. A relatively thin layer of the material 15 is fed to the rolls 10 from the hoppers 13, the thickness of the layer being determined and regulated by means of the vertically sliding doors 28. The central hopper 12 is also provided with sliding doors 29, arranged to be adjusted in dependence of the thickness of the layer of material 15 applied to the rolls.

With the embodiment illustrated in FIGS. 5 and 6, magnetic material 15 is fed from the hopper 11 to the input side of the rolls 10. The rolls 10 comprise a shell 18 of material having a low magnetic permeability and a core 19 of a material having high magnetic permeability. Arranged in spaced relationship between the shell 18 and the core 19 of each roll 10 are axially extending rows of electromagnets 30, comprising a core and a coil. The spaces 31 located between the electromagnets form passages for conducting a suitable coolant through the rolls. The coils of the electromagnets are preferably wound around the cores so that the north pole of the magnets in each alternate axial row thereof is located adjacent the shell 18 and the south pole of the remaining rows ofelectromagnets is located adjacent said shell. Preferably only those magnets located momentarily on the input side of the rolls 10 in front of and within the roll nip as the rolls rotate, for example the magnets indicated by the reference numeral 30', are connected to a source of current, via a commutator means. Such commutator means are well known in the art and are therefore not illustrated in FIGS. 5 and 6.

FIG. 7 illustrates an agglomerating rolling mill intended for relatively low rolling pressures, of which each roll 10 has the form of a cylinder which in construction is similar to one of the cylinders of a conventional magnetic separator. The rolls 10 comprise shells 18 of a material having low magnetic permeability and stationary arrays of magnets located so as to create magnetic fields in the rolls l0 and the magnetic mate rial 15 from the hopper 11 at the input side of the rolls and in the roll nip. As illustrated in FIG. 7, the arrays of magnets in the left roll 10 of the illustrated embodiment comprise permanent magnets 32 interconnected at their ends remote from the shell 18 by a yoke 33 comprising a material of good magnetic permeability. while the array of magnets in the right roll 10 in FIG. 7 comprises electromagnets 34, which are also interconnected at their ends remote from the shell 18 by meansof a yoke 33. The magnets 32 and 34 are disposed in spaced relationship peripherally of the rolls l0 'and additional magnets 32 and 34 may be arranged in rows along the length of the rolls, each alternate magnet in the peripheral direction of the rolls, and optionally also in the. longitudinal direction thereof, having its north pole located adjacent the roll shell 18, while the remaining magnets 32 and 34 have'their south pole located adjacent said shell.

With the agglomerating rolling mill illustrated in FIG. 8, magnetic material 15 is fed to the input side of the roll 10 by means of a hopper 11. The rolls are homogeneous and comprise a material of good magnetic permeability. Arranged around the hopper 11 and in close proximity of the rolls 10 is a magnetizing coil 35. To facilitate closing of the magnetic fieldon the outside of the coil 35, a yoke 36 can be arranged externally of the coil on each long side of the hopper 11 to extend along the length of the rolls 10. The yoke 36 comprises a material of good magnetic permeability, as illustrated with the dash lines in the Figure. The rolls 10 of the embodiment illustrated in FIG. 7 may be provided with a core of material of low magnetic permeability, if so desired.

With the agglomerating rolling mill illustrated in FIG. 9, in which the hopper 11 for supplying magnetic mate- 'rial to the input side of the rolls 10 has been omitted,

the whole of each roll 10, or at least the peripheral portion thereof, comprises a material of good magnetic permeability, and means are provided for-magnetizing said portion of at least one of the rolls 10, the upper roll of the embodiment illustrated in the Figure, to a single magnetic pole. In the illustrated example, the magnetizing means comprises a magnetizing coil 37 arranged around each neck of the upper roll 10. The magnetizing coils 37 are energized in opposite directions so that the entire upper roll forms a-north pole N, whereby the lower roll 10, or its peripheral portion, automatically forms a south pole S. The embodiment illustrated in FIG. 9 includes a yoke 38 comprising a material of good magnetic permeability arranged between the necks of the rolls 10 for collecting and closing the magnetic .circuit, although it will be understood that in practice the actual roll stand may be used to fulfil this ner such that the entire lower roll forms a magnetic "'s'o'u't'h'poleS."

With the embodiment illustrated in FIGS. 10 and 11, the whole of the rolls 10, or at least the peripheral portions thereof,comprise a material of good magnetic permeability. Magnetic material is fed to the input side of the rolls 10 by means of the hopper 11. Located the means 40 are connected together by means of a material 42 of good magnetic permeability.

It will be understood from the aforegoing that with the agglomerating rolling mills illustrated in FIGS. 5 ll the-attraction forces between the rolls 10 and the material 15 can be adjusted to a desired value by controlling the current to the magnetizing coils. Similarly, when as is normal with rolling mills the rolls are urged yieldingly towards each other with a predetermined force, the thickness of the cake formed during the rolling operation can also be adjusted to a desired value by'controlling the current to the magnetizing coils.

Although the invention has been described and illustrated with respect to agglomerating rolling mills having only one pair of co-acting compacting rolls 10, it will be readily understood that the invention can also be applied to agglomerating rolling mills having more than two co-acting compacting rolls and that the invention is not restricted to' the illustrated and described embodiments, but can be modified within the scope of the following claims.

I claim:

l. A method of agglomerating particulate material by compacting the material between co-acting rolls forming a roll nip wherein surface were on the rolls is substantially reduced, comprising:.

a.- coating at least a portion of at least one roll on the side of the one roll where the material passesinto "said nip with a'layer 'of a first' pa'r'ticulate magnetic material and retaining said layer on said portion of said roll by magnetic forces; I I v b. positively guiding a second particulate material into contact with said layer of first particulate magnetic material; and I a c. passing said first and second materials through said roll nipand under pressure to compact said materials and form a coherent cake thereofland d. disintegrating said coherent cake after said roll nip to form said cake into agglomerates of said particulate materials.

2. A method'according to claim 1, wherein said second material is magnetic and at least a portion of the second material forms said layer of first material, the remaining portion being material to be agglomerated.

3. A method according to claim 1, wherein said second material is substantially nonmagnetic and removing said layer of first material from said one roll passing through said roll nip, and successively applying to said one roll magnetic material forming said layer of first material to prevent a surface of said one roll from contacting the substantially nonmagnetic material.

4. A method according to claim I, wherein said second material is substantially nonmagnetic and including mixing the first magnetic material forming said layer with the substantially nonmagnetic material. 

1. A METHOD OF AGGLOMERATING PARTICULATE MATERIAL BY COMPACTING THE MATERIAL BETWEEN CO-ACTING ROLLS FORMING A ROLL NIP WHEREIN SURFACE WERE ON THE ROLLS IS SUBSTANTIALLY REDUCED, COMPRISING: A. COATING AT LEAST A PORTION OF AT LEAST ONE ROLL ON THE SIDE OF THE ONE ROLL WHERE THE MATERIAL PASSES INTO SAID NIP WITH A LAYER OF A FIRST PARTICULATE MAGNETIC MATERIAL AND RETAINING SAID LAYER ON SAID PORTION OF SAID ROLL BY MAGNETIC FORCES; B. POSITIVELY GUIDING A SECOND PARTICULATE MATERIAL INTO CONTACT WITH SAID LAYER OF FIRST PARTICULATE MAGNETIC MATERIAL; AND C. PASSING SAID FIRST AND SECOND MATERIALS THROUGH SAID ROLL NIP AND UNDER PRESSURE TO COMPACT SAID MATERIALS AND FORM A COHERENT CAKE THEREOF, AND D. DISINTEGRATING SAID COHERENT CAKE AFTER SAID ROLL NIP TO FORM SAID CAKE INTO AGGLOMERATE OF SAID PARTICULATE MATERIALS.
 2. A method according to claim 1, wherein said second material is magnetic and at least a portion of the second material forms said layer of first material, the remaining portion being material to be agglomerated.
 3. A method according to claim 1, wherein said second material is substantially nonmagnetic and removing said layer of first material from said one roll passing through said roll nip, and successively applying to said one roll magnetic material forming said layer of first material to prevent a surface of said one roll from contacting the substantially nonmagnetic material.
 4. A method according to claim 1, wherein said second material is substantially nonmagnetic and including mixing the first magnetic material forming said layer with the substantially nonmagnetic material. 